Shutters for pinhole detectors



June 13, 1967 l. MOSKOWITZ 3,325,648

SHUTTERS FOR PINHOLE DETECTORS Filed March 10, 1964 2 Sheets-Sheet 1 June 13, 1967 MOSKOWITZ 3,325,648

SHUTTERS FOR PINHOLE DETECTORS Filed March 10, 1964 2 SheetsSheet 2 "Q INVENTOR.

/sad0re Mos/row/fz United States Patent 6 3,325,648 SHUTTERS FOR PiNl-IOLE DETECTORS Isadore Moslrowitz, Baltimore, Md, assignor, by mesne assignments, to Bethlehem Steel Corporation, a corporation of Delaware Filed Mar. 10, 1964, Ser. No. 350,726 Claims. (Cl. 250-219) This invention relates to shielding means for use in apparatus for detecting imperfections in moving strip by photoelectric means, and more particularly to shutters of novel construction to be used in pinhole detectors.

Steel strip to be coated with another metal, e.g. tin, is inspected for pinholes prior to the coating operation. The strip, which is accepted or rejected by customers on the basis of the number of inholes detected per area of material inspected, can thus be used in less critical applications if the density of pinholes is greater than that which is acceptable to said customers.

Inspection is accomplished by means of a pinhole detector, which comprises a source of light positioned on one side of the strip and light-sensitive means aligned with said source and positioned on the other side of said strip. Pinholes are detected through the actuation of said light-sensitive means by light from said source which has passed through the pinholes in the strip.

Inasmuch as actuation of the light-sensitive means by light passing around an edge of the strip would result in false pinhole indications, pinhole detectors are provided with shielding means positioned adjacent each edge of the strip. For reasons of accuracy, the shielding means must be designed whereby the strip can be inspected to within a very small distance from its edges.

It is an object of this invention to provide pinhole detectors with shielding means constructed so that the probability of light actuating the light-sensitive means of said detectors without first passing through the strip being inspected is very small.

It is a further object of this invention to provide shielding means which permits accurate inspection of moving strip to within a very small distance from its edges.

I have discovered that the foregoing objects can be attained by providing shielding means which directs light from the source, in the vicinity of an edge of the strip, toward said light-sensitive means and diagonally inwardly of said edge. Thus, the light which impinges upon the strip area adjacent the edge does so at an angle whereby any reflected light is reflected inwardly, i.e. away from said edge and toward the center of the strip. Inasmuch as substantially no light impinges upon the strip area, in the vicinity of an edge, at angles which result in light being reflected outwardly, i.e. toward the edge of the strip, the probability of light being reflected around the edge of the strip and actuating the light-sensitive means of the detector is very small. Detection accuracy is consequently very high.

The features of the invention which I believe to be novel are set forth with particularity in the appended claims. Both the structure and the method of operation of the invention, as Well as further objects and advantages thereof, will be better understood by reference to the following description taken in connection with the drawings, in which FIGURE 1 is an isometric view of the shielding means and portions of the pinhole detector on which it is mounted.

FIGURE 2 is a plan view of the shielding means shown in FIGURE 1.

FIGURE 3 is a sectional view along the lines 3-3 of FIGURE 2.

Referring more particularly to FIGURE 1, a pinhole ice detector 113 is shown as comprising a detector head 11 and a detector base 12 between which a strip 13 travels. The head 11, shown in a raised or retracted position, is pivotally mounted on the base 12 by suitable means, e.g. brackets 14. The head is provided with a source of light (not shown) and a rectangular aperture 15 through which said light is emitted. In its operating position the head 11 rests upon block 16.

The base 12 contains light-sensitive means, e.g. a plu rality of photomultiplier tubes (not shown). The base is provided with a rectangular aperture 17 through which light may enter. The aperture 17 is of sufficient length to accommodate the largest width of strip it is desired to inspect, and is slightly narrower than the aperture 15. The aperture 17 maybe provided with a filter 18 adapted to transmit only light within the same frequency range as that emitted by the source housed in the detector head 11.

Mounted adjacent the edge of the strip 13 is shielding means 19. As shown in detail in FIGURES 2 and 3, said shielding means broadly comprises a shutter 20 comprising a first shield 21, a second shield 22, and a main body section 23. The rear of section 23 is provided with a pair of cylindrical apertures 24 and 25 into which a pair of rods 2s and 27 are inserted. Said rods are secured to section 23 by means of set screws 28 and 29.

The rear of the shielding means 19 comprises a tail plate 36. Mounted on said tail plate is a guide block 31 containing cylindrical apertures 32 and 33 in alignment with apertures and 25, respectively. The rods 26 and 27 extend through apertures 32 and 33, respectively.

Shutter 29 and block 31 are urged apart by means of coil sprin s 34 and 35 encircling rods 26 and 27, respectively. Section 23 and block 31 are provided with enlarged cylindrical apertures 36, 37, 38 and 3% in which the ends of said springs are housed. The ends of rods 26 and 27 are provided with stops 40 and 41, respectively, to limit the maximum distance between the shutter 24} and block 31.

The tail plate 30 extends a short distance beneath section 23 when shutter 20 is in its fully forward position, i.e. when the distance between the shutter and block 31 is a maximum. Thus, light cannot pass between the rear edge of section 23 and the forward edge of the tail plate 30.

Mounted on the detector base 12 is a bracket 42 with which a bolt 43 is threadedly engaged. The shielding means 19 is secured to the base 12 by tightening said bolt into frictional engagement with tail plate 30.

Also mounted on the base 12 is a guide plate 44. The tail plate 30 and the shutter 20 are provided with flanges 45 and 46, respectively, which extend downwardly along the sides of plate 44. Lateral movement of the shielding means 19 is thereby precluded.

The first shield 21, second shield 22, and main body section 23 are constructed to provide a housing 47 for a roller bearing 48. A cross section of roller bearing 48 is shown in FIGURE 3, wherein 49 is a wheel mounted on bearings 50 so as to revolve freely in housing 47 and to contact the edge of strip 13 at the periphery of the wheel.

The first shield 21 is provided with a slot 51 extending outwardly from the inner end of said shield. The second shield 22 is provided with a slot 52, transversely aligned with slot 51, and also extending outwardly from the inner end of said shield. Slot 52, which is deeper than slot 51, is provided with a plurality of louvers 53 angu-larly inclined whereby light from the source is directed toward the light-sensitive means and diagonally inwardly of the edge of the strip 13. Preferably, the louvers 53 are diagonally disposed with respect to the direction of strip travel. Thus, any place on the stri which, at a particular instant, is not fully illuminated because of a louver interposed between it and the light source, is fully illuminated at a later instant by reason of the diagonal disposition of said louver. In the embodiment shown in the drawings, the louvers are substantially V-shaped.

It is to be understood that the shielding means should be constructed of material having non-reflective surfaces. Preferably the entire shielding means, and in particular the louvers and shields, are provided With light-absorbing surfaces, e.g. by coating said surfaces with black paint.

The operation of the above-described apparatus is substantially as follows. The strip is first threaded through the apparatus and the shielding means adjacent each edge of the strip is positioned so that the shutter is approximately half way between its inward and outward limits of travel. The strip is then inspected in the usual manner. The pinhole detector, which has been described only briefly in connection with the novel shielding means of the invention, is conventional.

The strip being inspected is frequently characterized by variations in its width as Well as some lateral movement. However, the shutters maintain a constant position relative to the edges of the strip by reason of the abovedescribed construction of the shielding means.

The strip is accurately inspected to within a very small distance from its edges by reason of the light-directing louvers which greatly reduce the probability of light being reflected around the edges of the strip.

Changes and modifications of this invention will undoubtedly occur to those skilled in the art and I therefore do not wish to be limited to the exact embodiment shown and described but may use such substitutions, modifications or equivalents thereof as are embraced within the scope of my invention or as pointed out in the claims.

I claim:

1. In apparatus for detecting imperfections in a moving strip by photoelectric means, said apparatus comprising:

(i) a source of light positioned on one side of said strip,

(ii) light-sensitive means substantially aligned with said source and positioned on the other side of said strip,

(iii) an improved shutter positioned adjacent each edge of said strip; each improved shutter comprising;

(a) a first shield and a second shield, (b) said first shield extending inwardly of the A. edge of the strip between said strip and said light-sensitive means,

(0) said second shield extending inwardly of the edge of the strip between said strip and said source of light,

(d) a slot extending outwardly from the inner end of said first shield, and

(e) means on said second shield aligned with said slot for directing light from said source toward said light-sensitive means and diagonally inwardly of the edge of said strip.

2. The improvement as recited in claim 1, in which means (e) thereof comprises:

(a) a slot substantially aligned with the slot in said first shield,

(b) light-directing means mounted in said slot in said second shield,

(c) said light-directing means comprising a plurality of angularly inclined louvers.

3. The improvement as recited in claim 2, in which said louvers are diagonally disposed with respect to the direction of strip travel.

4. The improvement as recited in claim 3, in which said shields and louvers are provided with light-absorbing surfaces.

5. The improvement as recited in claim 3, in which said louvers are substantially V-shaped, said shutter is adapted to be moved transversely with respect to the direction of strip travel, and means is provided for maintaining the position of said shutter with respect to the edge of said strip substantially constant.

References Cited UNITED STATES PATENTS 6/1965 Binks 250219 7/1966 Brosious et a1 250237 X OTHER REFERENCES RALPH G. NILSON, Primary Examiner.

J. D. WALL, Assistant Examiner. 

1. IN APPARATUS FOR DETECTING IMPERFECTIONS IN A MOVING STRIP BY PHOTOELECTRIC MEANS, SAID APPARATUS COMPRISING: (I) A SOURCE OF LIGHT POSITIONED ON ONE SIDE OF SAID STRIP, (II) LIGHT-SENSITIVE MEANS SUBSTANTIALLY ALIGNED WITH SAID SOURCE AND POSITIONED ON THE OTHER SIDE OF SAID STRIP, (III) AN IMPROVED SHUTTER POSITIONED ADJACENT EACH EDGE OF SAID STRIP; EACH IMPROVED SHUTTER COMPRISING: (A) A FIRST SHIELD AND A SECOND SHEILD, (B) SAID FIRST SHIELD EXTENDING INWARDLY OF THE EDGE OF THE STRIP BETWEEN SAID STRIP AND SAID LIGHT-SENSITIVE MEANS, (C) SAID SECOND SHIELD EXTENDING INWARDLY OF THE EDGE OF THE STRIP BETWEEN SAID STRIP AND SAID SOURCE OF LIGHT, (D) A SLOT EXTENDING OUTWARDLY FROM THE INNER END OF SAID FIRST SHIELD, AND 